This invention concerns an arrangement for providing air bag deployment openings in interior trim structure. Inflatable cushion devices (commonly referred to as "air bags") have been devised for automotive vehicles, in which one or more air bags are stowed in respective storage spaces located within the passenger compartment. Typically a driver's side air bag is stored in a compartment in the center of the steering wheel and a passenger's side air bag is stored in a compartment behind the instrument panel. Upon detection of a relatively severe collision, the air bag or bags are very rapidly inflated to be deployed in positions to cushion the driver and/or passengers from injury-causing contact with the interior structure of the auto.
The air bags must be neatly stowed out of sight and so as to be resistant to tampering, yet able to deploy into the passenger compartment in an instant. This requires a sturdy closure panel for the deployment opening, which preferably minimizes the visual impression of the presence of the closure, and yet reliably opens under the wide range of ambient temperature conditions for which the auto is designed for use, over the entire useful life of the car.
Such closures are usually opened by the force exerted by the inflating air bag, and the deployment of the air bag must not be appreciably slowed by resistance to the opening of the closure. The considerable force applied by the inflating air bag must not result in fragmentation or separation of the closure, lest debris be projected towards persons in the passenger compartment.
The closure is of necessity exposed within the auto interior, and thus must be aesthetically compatible with the auto interior trim.
A vinyl skin covering is commonly applied to the instrument panel and other trim panel surfaces. Plastics such as vinyl while durable are relatively tough and resistant to tearing.
There has heretofore been proposed such closures in which doors are formed by a substrate panel overlain by a vinyl skin, with the skin ruptured by the deploying air bag forcing the substrate panels open. While preweakening of the skin has been utilized to facilitate tearing, it is difficult to achieve reliable tearing at the appropriate force level. U.S. Pat. No. 3,640,546 discloses a closure in which a pair of doors are covered by a covering skin, preweakened along a line of separation; which is ruptured when the doors are forced opened by the deploying air bag. The line of weakening is described as being accomplished by a reduction in thickness, perforating, or heating. Such a joint is not sufficiently sturdy to resist inward pressure applied by an occupant and also results in a visible seam. Furthermore, a consistent control over the depth of cut when scoring vinyl is not easily obtained, and a proper bursting strength is difficult to reliably achieve in production.
Other approaches have included positioning piercing pieces forced into the skin to initiate tearing action, but this creates a complicated design.